矩阵测光到底是如何工作的？在矩阵测光的情况下该如何曝光补偿？矩阵测光是一个能够猜测摄影意图用来point & shoot 的傻瓜模式么？很多人（包括KenRockwell）都提到D80的矩阵测光有过暴倾向，到底是否真是这样？
今天读到一篇文章对这个问题有了些详细的分析。
作者做了一个实验，以18%灰度板为背景，以纯白、纯黑、以及18%灰做前景，用矩阵测光的模式分别拍摄三张照片。结果是纯白前景的照片曝光不够，灰度前景的照片曝光正确，纯黑前景的照片过暴。结论是D80的矩阵测光模式加强了中心部位（我理解是聚焦点）的权重，保证中心部位按照18%的灰度进行曝光。这样的话在拍摄深色主体时会得到过暴的结果。原文引用如下：
Exposure
Good news, bad news, folks. Let’s start with the bad news, since there are plenty of contentious threads across the Nikon forums on the Internet talking about the issue: the matrix meter is more sensitive to what’s going on in the central area.
Say what? That’s bad news? Yes, it is for those of you who’ve shot with the D70, D100, D200, D1 series, D2 series, or any of the Nikon film bodies. That’s because all those other bodies are remarkably good at not being coerced into changing exposure based upon smallish non-middle gray things in the central area of the frame. The D50 was prone to changing exposure in those situations, and the D80 is even more prone to changing exposure due to middle subject tonal value. If you’re not following me, try the following: cut a diamond shape (like the AF sensor pattern) out of white paper, middle gray paper, and black paper. (I’m having you use a diamond shape so that you’ll frame them the same.) Now place each of those against a middle gray background, carefully framing so that the diamond exactly fits the AF sensor pattern. Voila: the gray background is underexposed with the white diamond in the center, properly exposed with the gray diamond in the center, and overexposed with the black diamond in the center. It’s that last one that’s problematic, in my mind. Overexposure means blown highlights that can’t be recovered, and the D80 is going to be prone to do just that with the matrix metering system any time you’ve got darker-than-middle-gray subjects in the center of the frame. Photo of the bride only? A little underexposed but easily savable. Photo of the groom only? Overexposed and not savable. Oops.
我感觉作者的实验可能不够严禁， 在这种实验情况下任何一个相机，任何一种测光模式都会得到同样的结果（白色欠暴、黑色过暴、18%灰色曝光正常）。但是结论可能是正确的，也就是说，D80的矩阵测光试图最大限度地保证主题根据18%灰度进行曝光。那么在使用矩阵测光时，简单地根据聚焦的主体按照白加黑减的原则进行曝光补偿。
需要做以下测试：
- 在背景、前景亮度一定的情况下，改变聚焦主体的位置，观察曝光情况；
- 在前景亮度一定的情况下改变背景亮度，观察曝光情况；
- 在背景、前景亮度一定的情况下改变前景大小，观察曝光情况。
